Modern aircraft require greater performance from their high lift devices while trying to minimise their structure and system impact. High lift systems need to provide a high lift to drag ratio during take-off, while achieving maximum lift and therefore maximum angle of attack at landing.
Associated with the performance constraints are structure and system requirements that are driving the design toward simpler, lighter and more compact devices.
Interference between high lift leading edge devices and internal structure (such as the front spar) and external structure (such as the engine nacelle and thrust reverser) needs to be avoided.
Conventional leading edge high lift devices are described in WO 2005/108205 A1 and U.S. Pat. No. 5,927,656. In WO 2005/108205 A1 the device is rotated about an axle between a stowed position and a deployed position. In the stowed position the device is sealed against the fixed leading edge of the wing, and in the deployed position a slot is formed between these elements. U.S. Pat. No. 5,927,656 describes a similar arrangement, although in this case the flap can also be deployed to an intermediate position in which there is little or no gap between the trailing edge of the device and the fixed leading edge.
A problem with these conventional arrangements is that only a simple rotation is possible. Therefore it is difficult to optimise position of the device in its various positions. A conventional approach to providing a more complex motion is to mount the device on a curved track, as described for example in U.S. Pat. No. 4,399,970. However such track mechanisms are complex, heavy, and take up a large amount of space.